A. Shukri

Measurement of mass attenuation coefficients of moderate-to-high atomic-number elements at low photon energies

Abstract Mass attenuation coefficients for 12 selected moderate-to-high atomic-number elements have been obtained from good-geometry measurements made at five 241Am photon energies of significant emission intensity. Particular interest focuses on measured values for photon energies close to absorption edges. Comparisons with renormalized cross-section predictions indicate agreement to within stated error limits for the majority of cases. Significant discrepancies (>10%) are noted for Ta at 17.8 and 26.3 keV and W at 59.5 keV. Some support for a discrepancy between measurement and theory for W in the region of 60 keV is found in the reported measurements of others.

Mass attenuation coefficients of natural Rhizophora spp. wood for X-rays in the 15.77–25.27 keV range

The mass attenuation coefficients (mu/rho) of Rhizophora spp. were determined for photons in the energy range of 15.77-25.27 keV. This was carried out by studying the attenuation of X-ray fluorescent photons from zirconium, molybdenum, palladium, silver, indium and tin targets. The results were compared with theoretical values for average breast tissues in young-age, middle-age and old-age groups calculated using photon cross section database (XCOM), the well-known code for calculating attenuation coefficients and interaction cross-sections. The measured mass attenuation coefficients were found to be very close to the calculated XCOM values in breasts of young-age group.

A study of Rhizophora spp wood phantom for dosimetric purposes using high-energy photon and electron beams

Previous scattering and depth-dose investigations involving use of the Malaysian hardwood Rhizophora spp have shown this medium to produce good agreement with measurements made in water. Present study extends the comparison, now including measurements of percentage depth-dose made for photons at 6MV and 5 and 12MeV electron beams. For the 6 MV photon and 5 MeV electron beams, discrepancies between percentage depth-dose for Rhizophora spp and water, at all depths, are found to be within 2.6 and 2.4% respectively. At 12 MeV electron energies, measured percentage depth-doses in Rhizophora spp beyond 3.5cm depth are found to be in significant discord with those for water. The absorbed dose in water measured in Rhizophora spp at d(max) for all three beams produces discrepancies of no more than 1.1% when compared with measurements made in water.

Total differential scattering cross-sections of 59.54 keV photons for elements in the range 29 ≤ Z ≤ 74

Abstract Using the 59.54 keV gamma rays emitted by the radionuclide 241 Am, total differential scattering cross-sections have been determined for eleven moderate to high atomic number elements. Measurements were performed using a standard back-scattering geometry arranged to obtain scattering angles of 145°, 154° and 165° and associated photon momentum transfers, 4.58 ≤ x ≤ 4.76 A −1 . High purity (>99.9%) foils of Cu, Zn, Zr, Nb, Mo, Ag, Cd, In, Sn, Ta and W were used as targets. Measurements have generally been found to be in accord with predictions to within a conservative uncertainty of 10%, predicted values being obtained as total differential scattering cross-sections based upon the tabulations of modified form factors corrected for anomalous scattering (ACMFF) and non-relativistic wave functions for incoherent scattering.

Photon-atom scattering of 26.4 and 59.5 keV gamma rays in Mo, Nb and Zr

Abstract Differential coherent scattering cross-sections have been experimentally determined with 0 (10%) error for the photon energies 26.4 and 59.5 keV, using an annular 100 mCi 241 Am source. The source is housed in a stainless steel holder fabricated to contain heavy tungsten alloy shielding and capped with a beryllium window. The measurements were performed using a standard back-scattering geometry set up to obtain scattering angles of 145° and 165°. Mo, Nb and Zr (Aldrich Chemical Company, Inc.) foils of better than 99.9% purity were used as targets in conjunction with a Hyper-pure Germanium detector. Measurements using another prominent line at 17.8 keV are not presented due to the fact that the intense fluorescence X-ray peaks overlap significantly with the coherent scatter peaks from the Mo and Zr targets and the incoherent peak due to the Nb target. Experimental data have been compared with theoretical predictions.

Determination of absorbed dose for photon and electron beams from a linear accelerator by comparing various protocols on different phantoms

Protocols developed for high-energy dosimetry IAEA (Technical Reports Series No. 277, 1997), AAPM (Med. Phys. 10 (1983) 741: Med. Phys. 18 (1991) 73: Med. Phys. 21 (1994) 1251), IPEMB (Phys. Med. Biol. 41 (1996) 2557), and HPA (Phys. Med. Biol. 28 (1983) 1097) have continued to enhance precision in dose measurements and the optimization of radiotherapy procedures. While recent dosimetry protocols, including those due to the IAEA and IPEMB, have made a number of improvements compared with previous protocols, it is further desirable to develop absolute dosimetry methods of dose measurements. Measurements based on careful implementation of procedures contained within the various protocols have been carried out in an effort to determine the extent to which discrepancies exist among the protocols. Dose in water at dmax was measured using cylindrical and parallel-plate ionization chambers for 6 MV photon beams and 5 and 12 MeV electron beams. Results obtained from the use of the AAPM and HPA protocols for 6 MV photon beams were found to be 0.9% larger and 0.1% smaller, respectively, than those measured following the IAEA protocol. Calibration dose measurements for 5 and 12 MeV electron beams in water phantoms were found to agree to within 1%, this being well within recommendations from the ICRU and other sources regarding the accuracy of dose delivery.

Incoherent scattering of 59.54 keV gamma rays by selected elements in the atomic region 29 ≤ Z ≤ 74

Abstract Incoherent scattering cross-sections for 11 moderate to high atomic number elements have been experimentally determined using 59.54 keV gamma rays emitted by the radionuclide 241 Am. Measurements were performed using a standard back-scattering geometry set up to obtain scattering angles of 145°, 154° and 165°. Resulting photon momentum transfers were in the range 4.58⩽ x ⩽4.76 A −1 . High purity (better than 99.9%) foils of Cu, Zn, Zr, Nb, Mo, Ag, Cd, In, Sn, Ta and W were used as targets. Results of measurements, good to within a conservative experimental uncertainty of 10%, reveal no systematic trend in departure from agreement with tabulated theoretical incoherent-scattering cross-sections based upon non-relativistic wave functions.

Applications of XRF, NAA and low-kV radiographic techniques in the study of body composition and diseased tissue

Abstract Members of this group have responded to a number of challenging health issues by attempting to devise sensitive XRF, NAA and low-kV radiographic measurement systems foboth in vivo and in vitro applications. These studies are generally either of toxicological importance, examine potential for diagnosing the presence of disease, or offer effective means for monitoring potentially harmful side-effects of therapy. Particular examples include the in vivo XRF investigation of human skeletal uptake of Pb in working and living environments, in vivo XRF monitoring of elevated levels of Fe in skin (indicating the presence of an undesirable side-effect of the treatment of thalassaemia), in vivo NAA monitoring of elevated levels of Al in bone (indicating an undesirable side-effect of the treatment of chronic renal failure) and in vitro characterization, by means of low-kV imaging, of a range of calcification parameters in healthy and diseased breast tissue. The latter investigation has been conducted in association with an in vitro NAA study of concentrations of trace elements in the same types of tissue. Figures of merit for the various measurement systems have been obtained in terms of minimum detectable levels and concentrations (MDLs and MDCs) and where applicable, image related parameters.

Determination of Cu, Zn and Pb in scalp hair from a selected population in Penang using the XRF method

The state of Penang encompasses an industrial region with a potential for the existence of a variety of industrial pollutants. Such pollutants would certainly have a possible impact effect on the environment and the people. The determination of trace elements levels in hair which is well known as a method for environmental exposure monitoring, evaluation of heavy metal poisoning, assessment of nutrient levels and disease diagnoses, is chosen here as the method to determine the possible exposure to possible pollutants in the form of unwanted trace elements. The natural levels of trace elements in hair are hence monitored first as reference values for the assessment of the possible human contamination levels. In this work the concentrations of Cu, Zn and Pb in human scalp hair of 50 residents of Penang were determined using XRF. The results of this study were compared with the results obtained in other cities where such measurements have also been carried out.

A simplified approach for exit dose in vivo measurements in radiotherapy and its clinical application

This is a study using LiF:Mg;Ti thermoluminescent dosimeter (TLD) rods in phantoms to investigate the effect of lack of backscatter on exit dose. Comparing the measured dose with anticipated dose calculated using tissue maximum ratio (TMR) or percentage depth dose (PDD) gives rise to a correction factor. This correction factor may be applied to in-vivo dosimetry results to derive true dose to a point within the patient. Measurements in a specially designed humanoid breast phantom as well as patients undergoing radiotherapy treatment were also been done. TLDs with reproducibility of within ±3% (1 SD) are irradiated in a series of measurements for 6 and 10 MV photon beams from a medical linear accelerator. The measured exit doses for the different phantom thickness for 6 MV beams are found to be lowered by 10. 9 to 14. 0% compared to the dose derived from theoretical estimation (normalized dose at dmax). The same measurements for 10 MV beams are lowered by 9. 0 to 13. 5%. The variations of measured exit dose for different field sizes are found to be within 2. 5%. The exit doses with added backscatter material from 2 mm up to 15 cm, shows gradual increase and the saturated values agreed within 1. 5% with the expected results for both beams. The measured exit doses in humanoid breast phantom as well as in the clinical trial on patients undergoing radiotherapy also agreed with the predicted results based on phantom measurements. The authors’ viewpoint is that this technique provides sufficient information to design exit surface bolus to restore build down effect in cases where part of the exit surface is being considered as a target volume. It indicates that the technique could be translated forin vivo dose measurements, which may be a conspicuous step of quality assurance in clinical practice.